association
Intraclass correlation (ICC)
Assess absolute agreement among numeric ratings or repeated measurements.
Requirements
- two or more numeric measurement columns
- the same units measured by every rater
Avoid when
- categorical ratings
- systematic rater differences should be ignored
Formula
ICC(2,1) = (MS_subject − MS_error) / total variance
Interpretation
ICC(2,1) estimates the share of total measurement variance attributable to stable between-unit differences.
Worked example
Assess absolute agreement among three devices measuring the same specimens.
Open example datasets